The Enkephalinergic System and Ethanol Effects

Abstract Alcohol (ethanol) reinforcement involves the ethanol-induced activation of the endogenous opioid system (enkephalins, endorphins, and dynorphins). This activation may increase the hedonic value and the reinforcing effects of the drug. Ethanol-induced changes in opioidergic transmission may contribute to alcohol intoxication and to the neuroadaptive responses produced by the long-lasting exposure to ethanol. Opioidergic transmission is altered by ethanol at distinct levels. In adults, β-endorphinergic and enkephalinergic transmission, through activation of mu and delta opioid receptors, play a key role in ethanol reinforcement and high levels of alcohol-drinking behavior. In preweanling rats, Methionine-enkephalin content is increased in the prefrontal cortex, the nucleus accumbens, and other brain areas, as a consequence of short and moderate ethanol exposure during late gestation. Prenatal ethanol treatment also induces selective changes in the Methionine-enkephalin content in the prefrontal cortex and other regions of 30-day-old adolescent rats. Therefore, changes in mesocorticolimbic enkephalin expression are essential in ethanol reinforcement in offspring.